This invention relates to an apparatus and a process for molding, i.e., casting and manufacturing cast bullets for small ammunition, the metal typically being lead or lead alloy.
The making or manufacture of cast bullets using molten lead or lead alloy is an art or technology that goes back several hundred years following the invention of gun powder. In broad terms, bullets were cast, in one prior art process, by pouring molten lead or lead alloy into a mold consisting of two blocks with one half of the bullet-shape or form cut into the inner face of each mold half, the two halves, when assembled together, jointly forming a cavity. The mold halves or blocks were held together on handles and aligned by suitable means such as pins in the blocks or on carriers. Molten metal then is poured into the mold cavity with some excess metal being provided on the top to allow for shrinkage as the metal cools. Early bullet molds had a small hole through which the metal was poured forming a small stem or sprue. After the molten metal had solidified and the mold was opened, the bullet or bullets, as the case may be for multiple cavities, were allowed to drop out. The stem or sprue was cut flush with the end of the bullet using an appropriate means such as a pair of nippers. Some molds had nippers or other cutting means built into the mold handles.
The next step in the evolution of bullet casting was the development of a mold with an integral sprue cutter plate with a countersink in the top face of the sprue cutter and with a small hole or orifice at the bottom of the countersink through which the metal flowed into the mold cavity. In the case of multicavity molds there is a countersink with an orifice in the sprue cutter spaced to register with each mold cavity. An example of a prior art sprue cutter is U.S. Pat. No. 3,870,272. The sprue cutter concept had several advantages over the prior art. First it provided greater control of the pour of metal, second it allowed the riser or stem to be eliminated as the bottom face of the sprue cutter is directly adjacent to the bullet base (or nose of the bullet as is the case of nose pour bullet molds) and hence there is no riser. Thirdly, the sprue cutter cuts off the sprue before the bullets are dropped from the mold. This apparatus resulted in a significant increase in production rates and quality of the bullet. There are variations in the integral sprue cutter as above described. There are variations in the size of countersinks and orifice holes as well as the location of the sprue cutter pivot point. In addition, there are some gang mold sprue cutters having a plurality of bullet cavities and an equal number of countersinks with a narrow trough connecting the countersinks in the sprue cutter. This allows a choice of filling each cavity individually or filling one cavity and then allowing the metal to flow along the trough to the next cavity until it fills and hence from cavity to cavity until each one is filled. Prior art molds of this type with up to 10 cavities linked by a narrow trough have been supplied by (i) SAECO and (ii) Hensley and Gibbs. Problems with the above described gang mold are the high scrap rate produced by trapped air and poor bullet fillout and low shooting accuracy.
There are major disadvantages to the bullet casting apparatus and sprue cutters thus far described. When liquid metal is poured into a bullet mold directly through the orifice hole at the bottom of the countersink in a sprue cutter, it strikes the bottom of the mold cavity with enough velocity and force to cause splashing and turbulence. This effect throws metal up and around the sides of the mold cavity. The metal that is thrown up begins to solidify before the rest of the metal enters the cavity and can block the air vents before the mold cavity is filled. Also the turbulence causes internal and external air pockets or voids in the bullet and produces an imbalance condition wherein the center of gravity of the bullet is not exactly aligned with the longitudinal axis of the bullet. Depending upon the severity of the imbalance, the bullet's flight is adversely effected from a minor extent where the accuracy is adversely degraded to a major extent where the bullet will completely miss the mark or target. The air pockets above described occur randomly and unpredictably. The effect on the bullet's accuracy is directly proportional to the size and location of such voids or air pockets. Rigorous visual and weighing inspection of the bullets can assist in identifying bad bullets, but this is time consuming and expensive and further does not really address the problem of the bullet's center of gravity being out of alignment with the bullet's longitudinal axis. At this point of time commercial bullet casters visually inspect one-hundred percent of the product at least twice before packaging and shipping. One-hundred percent weight inspection is impractical due to the very high cost of high speed weighing equipment. It should be understood that tolerances of four-tenths of a grain to two grains, depending upon bullet weight, is the criteria for rejecting or accepting a bullet. The cost of high speed weighing equipment having this sensitivity is prohibitive. Furthermore, this still leaves the commercial caster and the consumer with the problem of hidden internal voids with the resultant effects on the bullet's performance and accuracy as aforesaid.